While I am vehemently opposed to abortion, I am not opposed to capital punishment. I am also unconcerned about what will be done with my body when I am through using it. It’s a Christian thing.
Perhaps the objections have more to do with the dehumanizing of people who see (or seek) this "art" than the dehumanizing of the bodies.
“It’s just your husk, son ... your mortal husk.”
That said, “Man is a creature composed of body and soul, made to the image and likeness of God.” Your body is not just the residence for your soul, but an equal part of your humanity. Debasing the body while you’re alive, or after you’re dead, disrespects God’s creation.
You’ll die, and you’ll rot, but that doesn’t mean it’s appropriate to treat the human body, living or dead, as if it’s an eggplant. Your body will be resurrected, to eternal life or eternal damnation, but the eggplant is just compost.